I have been a Lexus owner for many years and used this forum for a lot of help and advice with my SC 300 and is300 issues so hear goes . I bought my wife a 2000 AWD RX 300 with 72000 miles on it , the car had a sludge issue in the motor and I replaced it and the car runs great . Yesterday my wife called and said the car was making squealing noises and jerking some I thought maybe coil pack went bad or something so I went over to her work to check it out and drove the car around the block
and it started shifting funny and making a noise sounded like a belt squealing but stronger if that makes sense . Fast forward to last night the car quit on her on her way home . I went to pick up on my trailer and the car would move in gear but just for a few minutes then act like it was in neutral ,if you stop and wait it will go back in reverse or drive but again for a short time . My question is in the trans toast or can I try to fill fluid ,clean or replace filter etc . I have been looking at many post but none seem to have my particular symptoms . The fluid was full and red and not burnt smelling. Sorry for long post and appreciate any help or links anyone can give me. I bought this car to replace her 2013 sonata turbo because we needed more room for grandkids and so she wouldn't have any issues so I'm very surprised that my Lexus tranny is jacked at 75000 miles. Tom

 

Drop the oil pan and see whats in there. But it sounds like its toast.

 

Look for metal parts in the bottom of the pan if there are none can try replacing the filter I would fill it up with Max life synthetic transmission fluid get it at Walmart. You can buy 4 quarts for around $25 in a 4 quart bottle I would also run it then do a drop and fill using the drain plug in the transmission pan. It holds approximately 4 quarts I would do three more change outs so that you have about 95% clean oil good luck. Each time you do eight drop and fill taken on the road for about 15 miles if it's working then do another drop and fill this way you makes up the oil really well.I bought a 2001 RX 300 with the planetary gears singing opera in low gear I know they're about to go out I still did 4 change outs of Max Life synthetic transmission oil since last September. So far using synthetic oil the whining noise has dropped a little I find that Max Life does work great in my 2001 RX300 I think I can squeeze another year on the trans before I replace it. My trans guy Tustin Transmission here is So Cal has the planetary gears ends welded to stop them from failing this is the biggest problem with the first early RX 300 from what I can see.

 

I had the whining noise though in my case the transmission was still shifting just fine.
Dropping the pan and doing the full DIY on the transmission fluid (changed the filter and ~7 Quarts of Oil) helped my car in removing the squealing/whining sound.
So i would recommend that you try a full DIY and see if things improve, otherwise as also indicated above the Transmission might be already a .gone :-(
Here is the link to the problem that i had.

https://www.clublexus.com/forums/rx-...ing-noise.html

 

The factory ATF should've been changed at 60K even though Lexus claims it's "lifetime" fluid. Also, 1st gen RX are known for their weak tranny.
As for your question, it's most likely toast. I had a similar experience, while driving car lost all power to wheels. Had to down shift/park and back to D for gears to work again. Did that for a week.
Result? Tranny replaced at 210K.

 

What is your milage expectation for a trouble free auto trans with proper care and maintenance? 25 years ago it used to be 100k miles.

Salim

 

I heard that the lifetime ownership of a car is about 75,000 miles five years according to the salesman at Lexus most of us drive our cars 150,000 to 300,000 miles that's our lifetime. You need to change the oil in your transmission like Aznlapin suggested above I use Max life from Vavoline Oil, I buy it at Walmart in the gallon container for around 20 some dollars. If you can get to a good transmission shop see if they will let you bring your own Max life transmission fluid let them change it out for you they can do a drop and fill. I recommend having the filter changed at 60,000 miles don't forget the power steering fluid you can also use Max life there which is a fully synthetic transmission fluid.